The present invention relates to a gear pump and a liquid injection apparatus incorporating a gear pump.
A gear pump is generally superior to other types of pumps in that it has a simple configuration. FIG. 1 shows a conventional gear pump 100. The gear pump 100 has a drive gear 103 and a driven gear 104 accommodated in an accommodation chamber 102, which is formed in a housing 101 (refer to, for example, Japanese Laid-Open Patent Publication No. 8-093657). The drive gear 103 and the driven gear 104 are rotatably supported by rotation shafts 105 and 106, respectively. A suction chamber 110 and a discharge chamber 112 are defined in the accommodation chamber 102.
The rotation shaft 105 extends through a shaft hole (not shown) formed in the housing 101 and is received by a shaft hole 107 of the drive gear 103. Part of the rotation shaft 105 projects out of the housing 101. The rotation shaft 106 is received by a shaft hole 108 formed in a central part of the driven gear 104 and a shaft hole (not shown) of the housing 101.
When the drive gear 103 and the driven gear 104 are rotated, the liquid in the suction chamber 110 is transferred while being enclosed in the space defined by the teeth of the drive gear 103 and the inner surface 111 of the accommodation chamber 102 and the space defined by the teeth of the driven gear 104 and the inner surface 111 of the accommodation chamber 102 to be sequentially discharged to the discharge chamber 112.
In the prior art, the liquid may flow back from the discharge chamber 112 to the accommodation chamber 102 or leak from gaps between components inside the gear pump 100. This would lower the pumping efficiency of the liquid. The pumping efficiency of the liquid may be improved by machining the gears 103 and 104 and the housing 101 with accuracy so as to minimize the gaps between each of the gears 103 and 104 and the accommodation chamber 102. However, the machining of the gears 103 and 104 and the housing 101 with high accuracy increases the manufacturing cost and the number of manufacturing steps.